1. Field of the Invention
The present invention relates to silver halide photographic emulsions, and, more particularly, to silver halide photographic emulsions containing the combination of at least one organic thioether compound and at least one thiosulfonic acid compound.
2. Description of the Prior Art
It is well known to use organic thioether compounds as a solvent for silver halide or chemical sensitizers, etc., in the preparation of a silver halide photographic emulsion.
For example, a technique for preparing a so-called monodisperse emulsion having a uniform silver halide particle size by allowing an organic thioether compound to be present during precipitation and during physical ripening in the preparation of a silver halide photographic emulsion (hereafter simply referred to as an "emulsion") is disclosed in U.S. Pat. Nos. 3,271,157, 3,531,289, 3,574,628, etc.
Further, a technique for increasing the photographic sensitivity of an emulsion by allowing an organic thioether compound to be present during chemical ripening, etc., in the preparation of an emulsion is disclosed in U.S. Pat. Nos. 2,521,926, 3,021,215, 3,038,805, 3,057,724, 3,062,646, 3,574,709, 3,622,329, 3,625,697, etc.
However, if an organic thioether compound is present during the preparation of emulsions, there is a tendency for fog to be increased.
In order to prevent this fogging due to the presence of organic thioether compounds, for example, techniques for precipitating at a pH below 4 or super-purifying organic thioether compounds are known. However, all of these techniques are disadvantageous since the effects achieved are insufficient or they are not practical on an industrial scale.